Determining the Right Generator Size for Your Home
To calculate the right generator size, you'll need to:
1 Make a List of Essential Items
First, identify what you absolutely need to power. Common essential items include:
Refrigerator: 600-800 watts running (higher at startup)
Sump pump: 750-1500 watts running
Furnace fan: 800 watts running
Well pump: 1000-2000 watts running
Window AC: 1000-1500 watts running
Lights: 60-600 watts (depends on number and type)
Phone chargers/electronics: 25-200 watts
2. Consider Starting Watts
Many appliances need 2-3 times their running wattage to start up. For example:
A refrigerator that runs at 800 watts might need 2400 watts to start
A sump pump running at 800 watts might need 2000 watts to start
3. Calculate Total Needs
Add up:
Running watts of items you'll use simultaneously
Highest starting watt requirement of any single item
Add 20% safety margin
For example:
Running: Fridge (800W) + Lights (400W) + Furnace (800W) = 2000W
Starting: Fridge needs 2400W to start
Add 20% to 2400W = ~3000W
Therefore, you'd need at least a 3000-watt generator in this case.
Common Size Categories:
2000-4000 watts: Good for camping, basic home backup (few appliances)
5000-7500 watts: Can run most essential home systems
8000-12000 watts: Whole-house coverage for medium homes
15000+ watts: Large homes or commercial applications
Special Considerations:
240V appliances (well pumps, electric ranges) need special generator capabilities
Sensitive electronics may need clean power from an inverter generator
Consider future needs - buying slightly larger gives flexibility
Climate matters - AC units in hot areas or heating in cold regions need extra capacity